Stabilized and transistorized ignition system for internal combustion engines

ABSTRACT

A transistorized ignition system for internal combustion engines is provided with a first voltage divider including a Zener diode for establishing a fixed voltage standard and with a second voltage divider to which said fixed voltage standard is applied. The second voltage divider includes a series arrangement of a fixed resistor and a temperature sensitive resistor and thus provides a set voltage that varies with temperature. This voltage is compared with a voltage proportional to the current flow in the primary winding of the ignition coil. This current flow is regulated by cascade connected transistors in accordance with the set point or set voltage established by said second voltage divider.

United States Patent Brungsberg [75] Inventor: Heinrich-Josef Brungsberg,

Ludenscheid, Germany [73] Assignee: Brown, Boveri & Cie. A.G.,

Mannheim, Germany [22] Filed: June 3, 1974 [21] App]. No.: 480,543

[30] Foreign Application Priority Data June 12, 1973 Germany v. 2329917 [52] US. Cl 123/148 E; 315/209 T [51] Int. Cl. F02p l/00 [58] Field of Search 123/148 E; 315/209 T [5 6] References Cited UNITED STATES PATENTS 3,605,713 9/1971 Le Masters 123/148 E [4 1 Aug. 26, 1975 3,745,985 7/1973 Hohne 123/148 E Primary Examiner-Charles J. Myhre Assistant Examiner-Ronald B. Cox

Attorney, Agent, or Firm-Erwin Salzer [57] ABSTRACT A transistorized ignition system for internal combustion engines is provided with a first voltage divider including a Zener diode for establishing a fixed voltage standard and with a second voltage divider to which said fixed voltage standard is applied. The second voltage divider includes a series arrangement of a fixed resistor and a temperature sensitive resistor and thus provides a set voltage that varies with temperature. This voltage is compared with a voltage proportional to the current flow in the primary winding of the igni tion coil. This current flow is regulated by cascade connected transistors in accordance with the set point or set voltage established by said second voltage divider.

4 Claims, I Drawing Figure STABILIZED AND TRANSISTORIZED IGNITION SYSTEM FOR INTERNAL COMBUSTION ENGINES BACKGROUND OF THE INVENTION This invention relates to a transistorized ignition system for internal combustion engines including a d-c power supply, an interrupter and an ignition coil in which system opening of the interrupter and interruption of the charging current result in conversion of the energy stored in the primary winding into a high voltage in the secondary winding sufficient to be used for ignition purposes.

The present application relates to an improvement of the ignition system which is described in my copending patent application filed 01/09/74; Ser. No. 431,832 for IGNITION SYSTEM FOR INTERNAL COMBUS- TION ENGINES. The object of the system described in that application is to stabilize the ignition energy and the secondary or ignition voltage available and to maintain the same as constant as possible, even ifthe voltage of the d-c power source, or battery, should be less than normal, and to achieve this end for the entire range of rpm at which the internal combustion engine is capable of operating. To this end a main or power transistor and a negative feedback resistor are arranged in series with the primary winding of the ignition coil. The collector of the main or power transistor is connected to one end of the primary winding of the ignition coil, and the emitter of that transistor is connected to the negative feedback resistor. The base of the aforementioned main or power transistor is connected to the collector of an auxiliary or control transistor, and the emitter of the latter is connected to a terminal of a d-c power sup ply.

The system disclosed in my above patent application allows a certain stabilization of the charging current of the primary winding of the ignition coil. Because the characteristics of the components of the system may change, the amplification factor may change, and because of unavoidable manufacturing tolerances, the stabilizing effect of the circuitry is subject to certain limitations. To be more specific, changes of the voltage level of the d-c power supply in the order ofi30% may result in variations of the charging current of the primary winding of the ignition coil up to i The principal object of the present invention is to reduce the range of possible variations of the charging current to a minimum, and to improve starting at relatively low temperatures. Further objects of the present invention consist in providing means which assure automatic de-energization of the primary winding of the ignition coil after the internal combustion engine has stopped to operate. Still a further object of the invention is to provide means for precluding damage to semiconductor elements of the circuitry by applying the wrong polarity of a d-c power source to their terminals.

SUMMARY OF THE INVENTION An ignition system embodying this invention includes a pair of power supply terminals to which a dc power supply or battery is intended to be connected. A first voltage divider connected to said d-c power supply terminals includes a series arrangement of a first resister and of a Zener diode. A second voltage divider is connected across the aforementioned Zener diode, and includes a series arrangement of a second resistor having a substantially fixed ohmic value and of a third resistor having an ohmic value that changes substantially with changing temperatures. The circuitry further includes a first transistor and a second transistor each connected with the base thereof to said second voltage divider. The collectors of said first transistor and of said second transistor are interconnected, and a third resistor is arranged in the base-emitter current path of said second transistor. The ignition system further includes an ignition coil having a primary winding energized from said d-c power supply terminals and a secondary winding. In addition to the above a system embodying this invention includes a fourth transistor and a feedback resistor arranged in series with said primary winding of said ignition coil. Said fourth transistor is under the control of said third transistor and controlls the current flow through said primary winding of said ignition coil. Finally the system includes a diode for applying the potential prevailing across said feedback resistor to the emitter of said second transistor.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a circuit diagram of an ignition system embodying the present invention.

DESCRIPTION OF PREFERRED EMBODIMENT In the drawing numeral 1 has been applied to indicate an interrupter. The way in which interrupter 1 is connected into the circuit will be considered below in detail. Numeral 2 has been applied to indicate a d-c power supply, or battery, having an upper positive terminal and a lower negative terminal. The positive terminal of battery 2 is connected by way of diode 29 to one end of the primary winding 9a of an ignition coil 9 including, in addition to the primary winding 9a, a secondary winding 9b. Main power transistor 7 and negative feedback resistor 8 are arranged in series with primary winding 9a, the collector 7c of transistor 7 being connected to primary winding 9a and the emitter 7a of transistor 7 being connected to resistor 8. Numeral 4 has been applied to indicate a control or auxiliary transistor whose emitter 4a is connected to the positive terminal of battery 2, and whose collector 4c is connected to the base 7b of transistor 7. Zener diode 13 is shunted across a portion of the primary winding 9a of the ignition coil 9, transistor 7 and resistor 8. To this end the primary winding 9a of ignition coil 9 is provided with a tap. Closing of interrupter 1 establishes a current path from the positive pole of battery 2 by way of resistor 19 and Zener diode 40 to ground. This current path includes diode 29. It will be apparent that resistor l9 and Zener diode 40 form a voltage divider dividing the voltage of battery 2. The voltage across components l9 and 40 is stabilized by the action of Zener diode 40. Reference numerals 38 and 39 have been applied to indicate two serially connected resistors which form a second voltage divider, the stabilized voltage across Zener diode 40 being applied across resistors 38 and 39. The latter has a fixed ohmic value, and the former changes with temperature, or is temperature sensitive. The set point, or set voltage value, of the system is that prevailing at a point between resistors 38 and 39. This voltage is applied to the base 35b of a transistor 35. The emitter circuit of transistor 35 includes the emitter 35a and the resistor 37. The potential across feedback resistor 8 is applied by the intermediary of diode 36 to the emitter 35a of transistor 35.

Reference numeral 13 has been applied to indicate a Zener diode connecting a tap of winding 9a to the negative pole of battery 2 and reference numeral has been applied to indicate a resistor interconnecting base 7b and emitter 7a.

The invention further provides means for turning off the primary winding 9a of the induction coil 9 when the internal combustion engine is not operating. This precludes overheating when the contacts of the interrupter 1 remain accidentally in the closed or engaged position thereof. A means to this end is the auxiliary or pretransistor 30 with its emitter 30a, its base 30b and its collector 30c. A point between resistor 19 and Zener diode 40 is connected to the base 30b of transistor 30 by the intermediary of capacitor 33 and resistor 31. A point intermediate capacitor 33 and resistor 31 is connected by diode 32 to the line which connects battery 2 to winding 90. The emitter 30a of auxiliary transistor 30 is connected to the base 4b of transistor 4, and the collector 30c of transistor 30 is connected to the collector 35c of transistor 35.

It will be apparent from the above that the circuitry described differs from the circuitry disclosed in the above referred-to patent application by the addition of an amplifying stage. This makes it possible to sufficiently increase the ignition energy during the starting period of an internal combustion engine.

As long as the set point, or set voltage, applied to the base 35b of transistor 35 exceeds to the feedback voltage across resistor 8, the auxiliary control transistor 35 is fully turned on. When the voltage across resistor 8 and the set voltage are equal, the charging current of winding 9a of ignition coil 9 assumes a predetermined value. In this way it is possible to limit variations of the charging current to the order of 2-3%, while the voltage of the d-c current supply undergoes changes in the order of i 30%. When the internal combustion engine is started at a relatively low temperature, the ohmic value of resistor 38 is high, resulting in a high set voltage at the base 35b of transistor 35. Under such conditions the actual value across resistor 8 ought to rise, and such rise results from an increase of the current energizing primary winding 9a. As the temperature of the internal combustion engine rises, the ohmic value of resistor 38 and the voltage at 35b decrease, and so does the energizing current of winding 9 a. When the temperature of the motor block varies between minus 40 C and 110 C, the charging current changes about 20%.

Considering now what happens when the operation of the internal combustion engine is interrupted or stopped, and the contacts of interrupter 1 remain in engagement. When the contacts of interrupter 1 are closed, capacitor 33 is entirely discharged. When the capacitor 33 is re-charged, a substantial current flows through the base 30b of transistor 30, and the latter is fully turned on. As the capacitor 33 is gradually charged, the base current of transistor 30 decreases and becomes finally zero. Thus transistor 30 is turned off and the current flow through primary winding 9a becomes likewise zero since the transistor 4 is likewise turned off for lack of base current. This process involves a considerable time element, eg 2-3 sec. Hence no high voltage is induced in the secondary winding 9b of ignition coil 9. Upon separation of the contacts of the interrupter l the capacitor 33 is rapidly discharged in a circuit which includes diode 32 and resistor 19.

The time constants are selected in such a way that the above described disconnect system for motor standstill is ineffective at motor starting conditions of about 60 rpm.

In order to prevent destruction of solid state devices forming a part of the present circuitry by applying a voltage of wrong polarity to them during maintenance and repair operations, the system is provided with the diode 29 whose anode is connected to the positive terminal of battery 2 and whose cathode is connected to terminal 41 of resistor 19. Further connected to terminal 41 are the cathode of diode 32, the emitter 4a of control or auxiliary transistor 4 and one end of the pri mary winding 9a of ignition coil 9. The diode 29 provides permanent protection against applying another polarity than plus polarity to terminal 41.

Reference numerals 17 and 18 have been applied to indicate a pair of terminals on a housing for the system which has been indicated by a dash-and-dot line 28. Capacitor 15 inside housing 28 interconnects the lines of positive and negative polarity.

A line which interconnects two ends of windings 9a, 9b includes the resistor 16 and a revolution counter 24 is connected to one of its ends.

The protective capacitor 34 is shunted across power transistor 7 and across feedback resistor 8.

Reference numeral 22 has been applied to indicate a spark plug whose circuit is energized by the secondary or high voltage winding 9b of ignition coil 9. The circuit of spark plug 22 includes the resistors 25 and 26. Reference character 21 has been applied to indicate a distributor having an arc gap. The resistor 23 is shunted across the arc gap of distributor 21 and reference numeral 27 has been applied to indicate the capacitance of the line.

I claim as my invention:

1. An ignition system for internal combustion engines to be energized by a d-c power supply comprising a. a pair of d-c power supply terminals (17,18)

b. a first voltage divider circuit connected to said d-c supply terminals (17,18) and including a series arrangement of a first resistor (19), a Zener diode (40) and an interrupter (1);

c. a second voltage divider circuit connected across said Zener diode (40) and including a series arrangement of a second resistor (39) having a substantially fixed ohmic value and of a third resistor (38) having an ohmic value that changes substantially with changing temperatures;

d. a first transistor (30) and a second transistor (35) connected to said second voltage divider circuit with the bases (30b,35b) thereof, the collector (30c) of said first transistor (30) and the collector (35c) of said second transistor (35) being interconnected, and said third resistor (38) being arranged in the base emitter current path (35b,35a) of said second transistor (35);

e. a third transistor (4) under the control of said first transistor (30);

f. an ignition coil (9) having a primary winding (9a) energized from said d-c power supply terminals (17,18) and a secondary winding (9b);

a fourth transistor (7) and a feedback resistor (8) both arranged in series with said primary winding of said ignition coil (9), said fourth transistor (7) being under the control of said fliird transistor (4) and controlling the current flow through said primary winding (90) of said ignition coil (9); and h. a diode (36) applying the potential prevailing across said feedback resistor (8) to the emitter (35a) of said second transistor (35).

2. An ignition system as specified in claim 1 wherein the emitter (30a) and the base (4b) of said first and said third transistor (30,4) are interconnected, wherein the collector (4c) and the base (7b) of said third and fourth transistor (4,7) are interconnected and wherein said feedback resistor (8) is arranged in the collectoremitter current path (7c,7a) of said fourth transistor.

3. An ignition system as specified in claim 1 wherein a capacitor (33) is interposed in a lead from said first resistor to the base (30b) of said first transistor (30) to turn said first transistor (30) off when said capacitor (33) is fully charged, and wherein a discharge diode (32) is provided to discharge of said capacitor (33) in response to opening of the contacts of said interrupter (l) and interruption of current flow through said first voltage divider (19,40).

4. An ignition system as specified in claim 1 including a diode (29) interposed in a lead from one of said pair of d-c power supply terminals (17,18) to the end of said first voltage divider remote from the cathode of said Zener diode (40) thereof. 

1. An ignition system for internal combustion engines to be energized by a d-c power supply comprising a. a pair of d-c power supply terminals (17,18) b. a first voltage divider circuit connected to said d-c supply terminals (17,18) and including a series arrangement of a first resistor (19), a Zener diode (40) and an interrupter (1); c. a second voltage divider circuit connected across said Zener diode (40) and including a series arrangement of a second resistor (39) having a substantially fixed ohmic value and of a third resistor (38) having an ohmic value that changes substantially with changing temperatures; d. a first transistor (30) and a second transistor (35) connected to said second voltage divider circuit with the bases (30b,35b) thereof, the collector (30c) of said first transistor (30) and the collector (35c) of said second transistor (35) being interconnected, and said third resistor (38) being arranged in the base emitter current path (35b,35a) of said second transistor (35); e. a third transistor (4) under the control of said first transistor (30); f. an ignition coil (9) having a primary winding (9a) energized from said d-c power supply terminals (17,18) and a secondary winding (9b); g. a fourth transistor (7) and a feedback resistor (8) both arranged in series with said primary winding (9a) of said ignition coil (9), said fourth transistor (7) being under the control of said third transistor (4) and controlling the current flow through said primary winding (9a) of said ignition coil (9); and h. a diode (36) applying the potential prevailing across said feedback resistor (8) to the emitter (35a) of said second transistor (35).
 2. An ignition system as specified in claim 1 wherein the emitter (30a) and the base (4b) of said first and said third transistor (30,4) are interconnected, wherein the collector (4c) and the base (7b) of said third and fourth transistor (4,7) are interconnected and wherein said feedback resistor (8) is arranged in the collector-emitter current path (7c,7a) of said fourth transistor.
 3. An ignition system as specified in claim 1 wherein a capacitor (33) is interposed in a lead from said first resistor to the base (30b) of said first transistor (30) to turn said fIrst transistor (30) off when said capacitor (33) is fully charged, and wherein a discharge diode (32) is provided to discharge of said capacitor (33) in response to opening of the contacts of said interrupter (1) and interruption of current flow through said first voltage divider (19,40).
 4. An ignition system as specified in claim 1 including a diode (29) interposed in a lead from one of said pair of d-c power supply terminals (17,18) to the end of said first voltage divider remote from the cathode of said Zener diode (40) thereof. 